/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package javax.servlet.jsp.tagext;

import javax.servlet.jsp.*;

/**
 * The IterationTag interface extends Tag by defining one additional method that
 * controls the reevaluation of its body.
 * 
 * <p>
 * A tag handler that implements IterationTag is treated as one that implements
 * Tag regarding the doStartTag() and doEndTag() methods. IterationTag provides
 * a new method: <code>doAfterBody()</code>.
 * 
 * <p>
 * The doAfterBody() method is invoked after every body evaluation to control
 * whether the body will be reevaluated or not. If doAfterBody() returns
 * IterationTag.EVAL_BODY_AGAIN, then the body will be reevaluated. If
 * doAfterBody() returns Tag.SKIP_BODY, then the body will be skipped and
 * doEndTag() will be evaluated instead.
 * 
 * <p>
 * <B>Properties</B> There are no new properties in addition to those in Tag.
 * 
 * <p>
 * <B>Methods</B> There is one new methods: doAfterBody().
 * 
 * <p>
 * <B>Lifecycle</B>
 * 
 * <p>
 * Lifecycle details are described by the transition diagram below. Exceptions
 * that are thrown during the computation of doStartTag(), BODY and
 * doAfterBody() interrupt the execution sequence and are propagated up the
 * stack, unless the tag handler implements the TryCatchFinally interface; see
 * that interface for details.
 * 
 * <p>
 * <IMG src="doc-files/IterationTagProtocol.gif"
 * alt="Lifecycle Details Transition Diagram for IterationTag"/>
 * 
 * <p>
 * <B>Empty and Non-Empty Action</B>
 * <p>
 * If the TagLibraryDescriptor file indicates that the action must always have
 * an empty element body, by a &lt;body-content&gt; entry of "empty", then the
 * doStartTag() method must return SKIP_BODY.
 * 
 * <p>
 * Note that which methods are invoked after the doStartTag() depends on both
 * the return value and on if the custom action element is empty or not in the
 * JSP page, not on how it's declared in the TLD.
 * 
 * <p>
 * If SKIP_BODY is returned the body is not evaluated, and then doEndTag() is
 * invoked.
 * 
 * <p>
 * If EVAL_BODY_INCLUDE is returned, and the custom action element is not empty,
 * the body is evaluated and "passed through" to the current out, then
 * doAfterBody() is invoked and, after zero or more iterations, doEndTag() is
 * invoked.
 */

public interface IterationTag extends Tag {

	/**
	 * Request the reevaluation of some body. Returned from doAfterBody.
	 * 
	 * For compatibility with JSP 1.1, the value is carefully selected to be the
	 * same as the, now deprecated, BodyTag.EVAL_BODY_TAG,
	 * 
	 */

	public final static int EVAL_BODY_AGAIN = 2;

	/**
	 * Process body (re)evaluation. This method is invoked by the JSP Page
	 * implementation object after every evaluation of the body into the
	 * BodyEvaluation object. The method is not invoked if there is no body
	 * evaluation.
	 * 
	 * <p>
	 * If doAfterBody returns EVAL_BODY_AGAIN, a new evaluation of the body will
	 * happen (followed by another invocation of doAfterBody). If doAfterBody
	 * returns SKIP_BODY, no more body evaluations will occur, and the doEndTag
	 * method will be invoked.
	 * 
	 * <p>
	 * If this tag handler implements BodyTag and doAfterBody returns SKIP_BODY,
	 * the value of out will be restored using the popBody method in pageContext
	 * prior to invoking doEndTag.
	 * 
	 * <p>
	 * The method re-invocations may be lead to different actions because there
	 * might have been some changes to shared state, or because of external
	 * computation.
	 * 
	 * <p>
	 * The JSP container will resynchronize the values of any AT_BEGIN and
	 * NESTED variables (defined by the associated TagExtraInfo or TLD) after
	 * the invocation of doAfterBody().
	 * 
	 * @return whether additional evaluations of the body are desired
	 * @throws JspException
	 *             if an error occurred while processing this tag
	 */

	int doAfterBody() throws JspException;
}
